Rat sarcoma model supports both "soil seed" and "mechanical" theories of metastatic spread.

Following injection into the portal venous or vena caval systems, tumour cells are held up almost exclusively in the liver or lung respectively, and subsequent outgrowth of tumour only occurs in these organs. Following systemic arterial injection, cells are distributed, and subsequently grow, in a variety of organs. However, the adrenal gland supports tumour growth from much fewer cells than the lung, and this is partly due to the fact the rate of tumour cell loss in the initial 48 h is very high in the latter compared to the former organ.